Name: 【TED-Ed】Schrödinger's cat: A thought experiment in quantum mechanics - Chad Orzel
Uploaded: 2014-11-30T12:53:22.000Z
Duration: 4 min 38 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

Austrian physicist Erwin Schrödinger is one of the founders of quantum mechanics,

but he's most famous for something he never actually did:

He imagined taking a cat and placing it in a sealed box

with a device that had a 50% chance of killing the cat in the next hour.

At the end of that hour, he asked, "What is the state of the cat?"

Common sense suggests that the cat is either alive or dead,

but Schrödinger pointed out that according to quantum physics,

at the instant before the box is opened, the cat is equal parts alive and dead,

It's only when the box is opened that we see a single definite state.

Until then, the cat is  a blur of probability,

This seems absurd,  which was Schrödinger's point.

He found quantum physics so  philosophically disturbing,

that he abandoned the theory he had helped make

As absurd as it may seem, though, Schrödinger's cat is very real.

If it weren't possible for quantum objects to be in two states at once,

the computer you're using to watch this couldn't exist.

is a consequence of the dual particle and wave nature of everything.

In order for an object to have a wavelength,

it must extend over some region of space,

which means it occupies many positions at the same time.

The wavelength of an object limited to a small region of space

So it exists in many different wavelengths at the same time.

We don't see these wave properties for everyday objects

because the wavelength decreases as the momentum increases.

If we took a single atom and blew it up to the size of the Solar System,

the wavelength of a cat  running from a physicist

would be as small as an atom  within that Solar System.

That's far too small to detect, so we'll never see wave behavior from a cat.

A tiny particle, like an electron, though,

can show dramatic evidence of its dual nature.

If we shoot electrons one at a time at a set of two narrow slits cut in a barrier,

each electron on the far side is detected at a single place at a specific instant,

But if you repeat this  experiment many times,

keeping track of all the  individual detections,

you'll see them trace out a pattern that's characteristic of wave behavior:

a set of stripes - regions with many electrons

separated by regions where there are none at all.

Block one of the slits  and the stripes go away.

This shows that the pattern is a result of each electron going through both slits

A single electron isn't choosing  to go left or right

This superposition of states also leads to modern technology.

An electron near the nucleus of an atom exists in a spread out, wave-like orbit.

and the electrons don't need to  choose just one atom

An electron in a molecule isn't on just atom A or atom B, but A+ B.

As you add more atoms, the electrons spread out more,

shared between vast numbers of atoms at the same time.

The electrons in a solid aren't  bound to a particular atom

but shared among all of them, extending over a large range of space.

determines the ways electrons move through the material,

whether it's a conductor or an insulator or a semiconductor.

Understanding how electrons are shared among atoms

allows us to precisely control the properties of semiconductor materials,

Combining different semiconductors in the right way

allows us to make transistors  on a tiny scale,

Those chips and their spread out electrons

power the computer you're using to watch this video.

An old joke says that the Internet  exists to allow the sharing of cat videos.

At a very deep level, though, the Internet owes its existance

to an Austrian physicist and his imaginary cat.